The present invention relates to a color selecting electrode for a color-picture tube for use in television receivers, computer terminal displays and the like, and a manufacturing method thereof.
In general, a color selecting electrode of a color-picture tube is comprised of a mask plate 1 made of a metal and a rectangular frame-shaped frame 2 made of a metal for stretchingly supporting the mask plate 1 as shown in FIG. 13. The mask plate 1 has a lot of slots 3 for letting electron beams pass therethrough, and four support end portions 1a through 1d of the mask plate 1 are welded to top surfaces of a pair of mutually-opposite long sides 4 and 5 and a pair of mutually-opposite short sides 6 and 7 of the frame 2.
In the above-mentioned welding process, the pair of long sides 4 and 5 and the pair of short sides 6 and 7 of the frame 2 are each pressed inward to be bent in a manner as shown in FIG. 14A. Then, while maintaining this state of bending, the support end portions 1a through 1d of the mask plate 1 are welded to the top surfaces of the four sides 4 through 7 of the frame 2 in a manner as shown in FIG. 14B, and thereafter the above-mentioned pressure is released in a manner as shown in FIG. 14C. As a result, a resilient force of the four sides 4 through 7 of the frame 2 exert a tension force to the mask plate 1 thereby allowing the mask plate 1 to be stretched with a high degree of flatness.
The tension force required for making the mask plate maintain a specified degree of flatness is of a great value of as much or about 10 kgf/mm.sup.2. Then, in order to generate such a great tension force, the mask plate is welded to the frame with each side of the frame bent inward, so that a resilient spring force is given to each of the sides. Then, the mask plate comes to have an elevated temperature upon collision of electron beams against the mask plate to consequently expand, with which the sides of the frame are deformed in a direction in which the degree of bending reduces. In the above-mentioned case, the mask plate extends more in the direction of the long sides than in the direction of the short sides. In contrast to the above, since the two short sides of the frame have a greater rigidity than the two long sides, the amount of displacement in the two short sides becomes much smaller than the amount of displacement in the two long sides, and the tension in the direction of the long sides becomes smaller than the tension in the direction of the short sides. Thus the tension in the direction of the long sides and the tension in the direction of the short sides of the mask plate are unbalanced at an elevated temperature, and this causes a problem that it is difficult to maintain the flatness of the mask plate at an appropriate value.
Furthermore, when a frame having a great plate thickness is used so as to increase the aforementioned rigidity, not only an increased weight results but also a support mechanism for supporting the color selecting electrode inside the color-picture tube is dimensionally increased, resulting in an increased totaled weight of the color-picture tube.